The present invention relates to an agent which minimizes a size of spherulites in a melt-processable crystalline fluorine-containing resin and can make a surface of a molded article smooth, a crystalline fluorine-containing resin composition containing the agent for minimizing spherulite size and a molded article obtained from the composition. The molded article of the present invention has a smooth surface and can be used suitably for various products, parts and containers in the field of semi-conductor manufacturing equipment.
Melt-processable crystalline fluorine-containing resins are excellent in heat resistance, chemical resistance and the like, and are used widely as a molding material in various fields. Particularly crystalline tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer (PFA) is, from the viewpoint of its excellent chemical and thermal stability and moldability, used as a material for a sheet, tube, joint, container, carrier, bellows, seal, etc. in the field of production of semi-conductors which is required to be free from contamination. In such a field of production of semi-conductors, as mentioned above, contamination by impurities and foreign matters (particles) is extremely required to be avoided, and it is required to make inside of equipment and inner surfaces of pipe and container as smooth as possible because particles are easily accumulated there.
However since PFA is a crystalline melt-processable resin, relatively large spherulites exist in a molded article obtained by melt-molding the resin. If many of such relatively large spherulites exist, it prevents a surface of the molded article from becoming smooth.
It is known that spherulites of PFA can be made smaller by increasing the number of nucleuses of spherulites, and basically the following two methods for minimizing a size of spherulite have been studied.
One is a method for blending polytetrafluoroethylene (PTFE) as an agent for forming a nucleus of spherulite into a PFA composition (JP-A-7-70397, JP-A-7-237257, JP-A-7-292200, JP-A-9-316266). There are two proposals of blending, as an additive, PTFE having a crystallization temperature of not less than 305xc2x0 C. and a crystallization calorie of not less than 50 J/g or PTFE crosslinked with ionizing radiation.
Another one is a method for blending, as a nucleus-forming agent, PFA having a low molecular weight or PFA having a low copolymerizing ratio of a perfluoro(alkyl vinyl ether) (PAVE) unit (JP-A-8-41267, JP-A-8-73689, JP-A-8-109225).
However in those methods, since crystallization temperatures of PFA having a low copolymerizing ratio of a PAVE unit and PFA having a low molecular weight are lower than that of PTFE, sufficient number of spherulite nucleuses are not formed and a spherulite size is not minimized sufficiently.
According to the method for blending PTFE as an agent for minimizing spherulite size into a PFA composition, though a spherulite size is minimized and through sight of an obtained molded article is improved, the molded article is wholly whity and transparency is not enough.
An object of the present invention is to provide the agent for minimizing size of spherulite in a melt-processable crystalline fluorine-containing resin such as PFA. The agent can not only minimize the size of spherulite in the resin and make highly smooth a surface of molded article obtained by melt-molding the resin but also decrease generation of particles.
While the conventional approaches are based on the use of highly crystalline agents for minimizing spherulite size such as PTFE and PFA having a high content of tetrafluoroethylene (TFE), the present inventors have made intensive studies as to converse approach, that is, use of an amorphous fluorine-containing polymer which has been considered not to be able to become a crystalline nucleus from a commonsense point of view. As a result, the present inventors have found that unexpectedly an amorphous fluorine-containing polymer has an excellent function of minimizing a spherulite size. Thus the present invention was completed. Though the reason for that is not clear, it is assumed that an amorphous fluorine-containing polymer decreases a growing speed of spherulite of a crystalline fluorine-containing resin and even in case of slow cooling, crystallization completes without growing the spherulite, and thus a size of produced spherulite is minimized.
Namely the agent of the present invention for minimizing spherulite size of a melt-processable crystalline fluorine-containing resin comprises an amorphous fluorine-containing polymer, preferably an amorphous fluorine-containing polymer having a glass transition temperature of not more than 25xc2x0 C.
As such an amorphous fluorine-containing polymer, there can be used selectively one having a compatibility with a crystalline fluorine-containing resin.
In case of minimizing spherulite size of a crystalline PFA as a crystalline fluorine-containing resin, a preferred amorphous fluorine-containing polymer to be used is an amorphous tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer.
Also as the agent for minimizing spherulite size of the present invention, there can be used one which contains a fluorine-containing multi-segment polymer comprising (A) an amorphous fluorine-containing polymer chain segment and (B) a crystalline fluorine-containing polymer chain segment comprising 80 to 100% by mole of tetrafluoroethylene (TFE) recurring unit and 0 to 20% by mole of a recurring unit represented by the formula (I):
CF2xe2x95x90CFxe2x80x94Rf1xe2x80x83xe2x80x83(I) 
wherein Rf1 is CF3 or ORf2, in which Rf2 is a perfluoroalkyl group having 1 to 5 carbon atoms.
In that case, the crystalline fluorine-containing polymer chain segment (B) may be a polymer chain segment consisting of TFE recurring unit or a polymer chain segment comprising TFE recurring unit and perfluoro(alkyl vinyl ether) (PAVE) recurring unit and containing PAVE in an amount of not more than 20% by mole.
In case where a crystalline PFA is used as a crystalline fluorine-containing resin, a preferred minimizing agent of spherulite size is an amorphous tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer or a fluorine-containing multi-segment polymer consisting of TFE recurring unit as the segment (B).
Thermal stability is improved by fluorinating those amorphous fluorine-containing polymer and fluorine-containing multi-segment polymer.
In case of minimizing spherulite size of vinylidene fluoride polymer (PVdF), examples of the amorphous fluorine-containing polymer to be used are, for instance, fluorine-containing elastomers having hydrogen atom such as vinylidene fluoride/hexafluoropropylene copolymer, vinylidene fluoride/hexafluoropropylene/tetrafluoroethylene copolymer, vinylidene fluoride/chlorotrifluoroethylene copolymer and vinylidene fluoride/chlorotrifluoroethylene/tetrafluoroethylene copolymer. Also there can be used the agent for minimizing spherulite size which contains a fluorine-containing multi-segment polymer having such an amorphous fluorine-containing polymer in its segment.
In case of a chlorotrifluoroethylene polymer (PCTFE), examples of the amorphous fluorine-containing polymer to be used are, for instance, vinylidene fluoride/chlorotrifluoroethylene copolymer, vinylidene fluoride/chlorotrifluoroethylene/tetrafluoroethylene copolymer, and the like. Also there can be used the agent for minimizing spherulite size which contains a fluorine-containing multi-segment polymer having such an amorphous fluorine-containing polymer in its segment.
The present invention also relates to the crystalline fluorine-containing resin composition prepared by blending those minimizing agents of spherulite size into a melt-processable crystalline fluorine-containing resin.
It is preferable that the minimizing agent is blended in an amount of 0.1 to 50 parts (part by weight, hereinafter the same) on the basis of 100 parts of the crystalline fluorine-containing resin.
Examples of the preferred melt-processable crystalline fluorine-containing resin are crystalline PFA (PAVE content: not more than 15% by weight), particularly PFA having a TFE/PAVE ratio of 90/10 to 99/1 in % by weight and a TFE/PAVE ratio of 96.0/4.0 to 99.6/0.4 in % by mole from the viewpoint of maintaining a high melting point.
Further the present invention relates to a molded article, for example, a tube, container, etc. obtained by melt-molding the above-mentioned crystalline fluorine-containing resin. It is preferable that the obtained molded article is one containing spherulites having an average spherulite size of not more than 5 xcexcm.
A major feature of the minimizing agent of spherulite size of the present invention is to use an amorphous fluorine-containing polymer or a fluorine-containing multi-segment polymer having an amorphous fluorine-containing polymer chain segment.
In the present invention, xe2x80x9camorphousxe2x80x9d means that when measuring with a differential scanning calorimeter (DSC), there is neither a melting peak temperature (Tm at heating) nor a crystallizing peak temperature (Tc at temperature decreasing) but there is observed a glass transition temperature (Tg). In other words, it means that there is no crystalline region substantially. On the other hand, xe2x80x9ccrystallinexe2x80x9d means that there are observed Tm and Tc.
Further the xe2x80x9camorphousxe2x80x9d segment (A) and xe2x80x9ccrystallinexe2x80x9d segment (B) of the fluorine-containing multi-segment polymer are such segments that the polymers having the same recurring units as those of the respective segments satisfy the above-mentioned definitions of xe2x80x9camorphousxe2x80x9d and xe2x80x9ccrystallinexe2x80x9d, respectively.
The crystalline fluorine-containing resin to be used in the present invention is a resin which is melt-processable and forms coarse spherulites at crystallizing. Therefore PTFE is excluded. Examples of the resin are, for instance, PFA (PAVE content: 1 to 10% by weight), PVdF, chlorotrifluoroethylene polymer (PCTFE), and the like. The minimizing agent of spherulite size of the present invention can be suitably used particularly for a crystalline PFA which is strongly required to give smoothness from the viewpoint of its application.
The amorphous fluorine-containing polymer and amorphous fluorine-containing polymer chain segment (A) in the fluorine-containing multi-segment polymer which are used in the present invention have a glass transition temperature (Tg). An amorphous polymer having Tg of not more than room temperature (25xc2x0 C.) is called an elastomer and one having Tg exceeding 25xc2x0 C. is called a resin. Use of an elastomer having Tg of not more than 25xc2x0 C. is preferable from the point that an effect of minimizing spherulite size is large, and the elastomer can be selected depending on its compatibility with a crystalline fluorine-containing resin to be used. However in the present invention, as the amorphous fluorine-containing polymer or amorphous fluorine-containing polymer chain segment (A), either of an elastomer having Tg of not more than 25xc2x0 C. and a resin having Tg exceeding 25xc2x0 C. may be used.
As the minimizing agent of the present invention, there are one comprising an amorphous fluorine-containing polymer and one comprising a fluorine-containing multi-segment polymer. First the former one comprising an amorphous fluorine-containing polymer is explained below.
As the amorphous fluorine-containing polymer, there are a fluorine-containing elastomer having Tg of not more than 25xc2x0 C. and an amorphous fluorine-containing polymer resin having Tg exceeding 25xc2x0 C.
Examples of the fluorine-containing elastomer are, for instance, perfluoro elastomers such as tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer; fluorine-containing elastomers having hydrogen atom such as vinylidene fluoride/hexafluoropropylene copolymer, vinylidene fluoride/hexafluoropropylene/tetrafluoroethylene copolymer, vinylidene fluoride/chlorotrifluoroethylene copolymer and vinylidene fluoride/chlorotrifluoroethylene/tetrafluoroethylene copolymer; and the like.
Among them, TFE/PAVE copolymer is preferred as the minimizing agent of spherulite size of PFA from the viewpoint of its compatibility with PFA. Examples of perfluoro(alkyl vinyl ether) (PAVE) to be used for the TFE/PAVE copolymer are perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), perfluoro(propyl vinyl ether), and the like. A content of PAVE is from 10 to 50% by mole, preferably from 20 to 50% by mole which is an amount where the TFE/PAVE copolymer has neither Tm nor Tc. A boundary between amorphous and crystalline is in the range of 10 to 20% by mole. If a polymer is amorphous in that range, the polymer can be used as the minimizing agent.
A fluorine-containing elastomer can be prepared by a process known as a process for preparing a fluorine-containing rubber (JP-B-58-4728, JP-A-62-12734).
For example, there is a process for emulsion-polymerizing the above-mentioned fluorine-containing monomer under pressure with stirring in an aqueous medium substantially under oxygen-free condition in the presence of an iodine compound, preferably diiodine compound and a radical polymerization initiator.
Represented examples of the diiodine compound are, for instance, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1,3-diiodo-2-chloroperfluoropropane, 1,5-diiodo-2,4-dichloroperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, 1,12-diiodoperfluorododecane, 1,16-diiodoperfluorohexadecane, diiodomethane, 1,2-diiodoethane, and the like. Those compounds may be used solely and can be used in combination with each other. Among them, 1,4-diiodoperfluorobutane is preferred. An amount of the diiodine compound is from 0.01 to 1% by weight on the basis of the whole amount of fluorine-containing monomers.
Also in the present invention, it is possible to copolymerize an iodine-containing monomer with the fluorine-containing elastomer. As an iodine-containing monomer, perfluoro(vinyl ether) compounds are suitable from the viewpoint of its copolymerizability. For example, perfluoro(6,6dihydro-6-iodo-3-oxa-1-hexene, perfluoro(5-iodo-3-oxa-1-pentene), and the like which are disclosed in JP-B-5-63482 and JP-A-62-12734 are suitable.
A polymerization temperature can be changed in the range of from about 10xc2x0 C. to about 100xc2x0 C. depending on property of an initiator to be used and a monomer. However at a temperature lower than 40xc2x0 C., a polymerization speed is low in case of using a persulfate solely. Also even in case of using a redox initiator containing sulfite, or the like, it is not preferable for an application for production of semi-conductors because the polymerization speed is low and besides a metal ion of a reducing agent remains in a polymer.
A radical polymerization initiator to be used may be the same as that which has been used for polymerization of a fluorine-containing elastomer. Examples of those initiators are organic and inorganic peroxides and azo compounds. Represented initiators are persulfates, carbonate peroxides, peroxide esters, and the like, and a preferred initiator is an ammonium persulfate (APS). APS may be used solely and can be used in combination with a reducing agent such as sulfites. In case where cleanliness is required, it is preferable not to use an initiator giving a metal ion, if possible.
In emulsion polymerization, various emulsifying agents can be used. Desirable are salts of carboxylic acid having a fluorocarbon chain or fluoropolyether chain from the viewpoint of preventing a chain transfer reaction with molecules of the emulsifying agent from arising during the polymerization. It is desirable that an amount of the emulsifying agent is from about 0.05% by weight to about 2% by weight, particularly from 0.2 to 1.5% by weight on the basis of added water.
A polymerization pressure can be changed in a wide range, usually in the range of from 0.5 to 5 MPa. The higher the polymerization pressure is, the higher the polymerization speed is. Therefore the polymerization pressure is desirably not less than 0.8 MPa from the viewpoint of an increase in production.
It is preferable that a number average molecular weight of the so-obtained fluorine-containing elastomer is from 5,000 to 750,000, further from 20,000 to 400,000, particularly from 50,000 to 400,000, from the viewpoint of good mixing with a crystalline fluorine-containing resin.
Examples of the amorphous fluorine-containing polymer resin having Tg exceeding 25xc2x0 C. are amorphous fluorine-containing polymers having a ring structure on a trunk chain thereof, for example, tetrafluoroethylene/fluorodioxole copolymers (cf. JP-B-63-18964, for example, tetrafluoroethylene/fluoro-2,2-dimethyl-1,3-dioxole copolymer, and the like); amorphous fluorine-containing polymers having a fluorine-containing alicyclic ring in its trunk chain and prepared by ring-forming polymerization of a fluorine-containing monomer having at least two polymerizable double bonds (for example, polymers obtained by ring-forming polymerization of perfluoro monomers such as perfluoro(allyl vinyl ether) and perfluoro(butenyl vinyl ether); or copolymers of those perfluoro monomers with radically polymerizable monomers such as tetrafluoroethylene, chlorotrifluoroethylene and perfluoro(alkyl vinyl ether)), and the like. Among them, from the viewpoint of heat resistance and chemical resistance, amorphous perfluoro polymers such as tetrafluoroethylene/perfluoro-2,2-dimethyl-1,3-dioxole copolymer and perfluoro(allyl vinyl ether) polymer are preferred.
Then the fluorine-containing multi-segment polymer is explained below.
The fluorine-containing multi-segment polymer to be used as the minimizing agent of spherulite size in the present invention comprises the amorphous fluorine-containing polymer chain segment (A) and the crystalline fluorine-containing polymer chain segment (B).
As the amorphous fluorine-containing polymer chain segment (A), there are elastomeric segment and resinous segment like the above-mentioned amorphous fluorine-containing polymer.
The elastomeric fluorine-containing polymer chain segment (A) is a segment having Tg of not more than 25xc2x0 C., for example, copolymers raised above as the fluorine-containing elastomers and can be prepared by the above-mentioned iodine transfer polymerization. In case of preparation by iodine transfer polymerization, an end of the segment is of perhalo type having iodine atom, and is used as a site for initiating the block copolymerization with the crystalline fluorine-containing polymer chain segment (B).
It is preferable that a number average molecular weight of the elastomeric fluorine-containing polymer chain segment (A) is from 5,000 to 750,000, further from 20,000 to 400,000, particularly from 50,000 to 400,000.
A particularly preferred segment as the elastomeric fluorine-containing polymer chain segment (A) is an elastomeric tetrafluoroethylene (TFE)/perfluoro(alkyl vinyl ether) (PAVE) segment comprising a TFE recurring unit and a PAVE recurring unit. In that case, a content of the PAVE recurring unit is an amount where the segment has Tg of not more than 25xc2x0 C. and does not have Tm and Tc, namely 10 to 50% by mole, preferably 20 to 50% by mole. A boundary between amorphous and crystalline is in the range of 10 to 20% by mole, and the segment in the amorphous range is used.
In case where the fluorine-containing multi-segment polymer is mixed to the matrix fluorine-containing resin, the crystalline fluorine-containing polymer chain segment (B) functions as an anchor so that the amorphous segment (A) does not become a particle and is not falling away from the matrix resin. Accordingly, the crystalline segment (B) is selected from those having good compatibility with the crystalline fluorine-containing resin. Concretely the crystalline segment (B) comprises a tetrafluoroethylene (TFE) recurring unit and a recurring unit represented by the formula (I):
CF2xe2x95x90CFxe2x80x94Rf1xe2x80x83xe2x80x83(I) 
wherein Rf1 is CF3 or ORf2, in which Rf2 is a perfluoroalkyl group having 1 to 5 carbon atoms. The recurring unit represented by the formula (I) is contained in an amount of not more than 20% by mole, preferably from 0 to 10% by mole, more preferably from 0 to 4% by mole. The amount of the recurring unit of the formula (I) exceeding 20% by mole is not preferable because the segment becomes amorphous and an anchor effect is insufficient. A boundary between amorphous and crystalline is in the range of 10 to 20% by mole, and the crystalline segment is used.
Examples of the monomer represented by the formula (I) are, for instance, hexafluoropropylene (HFP) and perfluoro(alkyl vinyl ether) (PAVE). Examples of PAVE are perfluoro(methyl vinyl ether) (PMVE), perfluoro(ethyl vinyl ether) (PEVE), perfluoro(propyl vinyl ether) (PPVE), and the like, and from the viewpoint of good compatibility with PFA, PPVE is particularly preferred.
Example of a particularly preferred crystalline segment (B) is a PTFE segment consisting a TFE recurring unit or a crystalline PFA segment.
The block copolymerization of the crystalline segment (B) with the amorphous segment (A) can be carried out, subsequently to emulsion polymerization of the amorphous segment (A), by changing to the monomer for the crystalline segment (B). A number average molecular weight of the crystalline segment (B) can be adjusted in a wide range of from 1,000 to 1,200,000, preferably from 3,000 to 400,000, particularly preferably from 10,000 to 400,000.
The so-obtained fluorine-containing multi-segment polymer mainly comprises a polymer molecule (B-A-B) in which the crystalline segments (B) are bonded to both sides of the amorphous segment (A) or a polymer molecule (A-B) in which the crystalline segment (B) is bonded to one side of the amorphous segment (A).
In the present invention, a proportion of the amorphous segment (A) to the crystalline segment (B) in the fluorine-containing multi-segment polymer may be selected in the above-mentioned molecular weight range. For example, a preferred weight ratio of A/B is 10/90 to 99/1, particularly 25/75 to 95/5. Also a molecular weight of the fluorine-containing multi-segment polymer may be one assuring good mixing with the crystalline fluorine-containing resin.
A particularly preferred segmented polymer is one having the following combination of segments.
(1) The amorphous segment (A) is TFE/PMVE (80/20 to 50/50 in % by mole ratio) having a number average molecular weight of 50,000 to 400,000.
The crystalline segment (B) is TFE/PPVE (100/0 to 80/20 in % by mole ratio) having a number average molecular weight of 10,000 to 400,000.
This segmented polymer is excellent from the points of minimizing a spherulite size of PFA, having an anchor effect and not lowering physical properties of PFA.
Also it is preferable that the minimizing agent of the present invention is subjected to treatment with fluorine gas in order to enhance heat resistance.
The treatment with fluorine gas is carried out by contacting fluorine gas to the minimizing agent. However a reaction with fluorine is very exothermic, and therefore it is proper to dilute fluorine with an inert gas such as nitrogen. An amount of fluorine in the fluorine gas/inert gas mixture is from 1 to 100% by weight, preferably from 10 to 25% by weight. A treating temperature is from 150xc2x0 to 250xc2x0 C., preferably from 200xc2x0 to 250xc2x0 C., and a fluorine gas treating time is from 3 to 16 hours, preferably from 4 to 12 hours. The gas pressure in treating with fluorine gas is in the range of 1 to 10 atm, and preferably an atmospheric pressure is used. When a reaction vessel is used at atmospheric pressure, the fluorine gas/inert gas mixture may be continuously passed to the reaction vessel. As a result, unstable end in the minimizing agent is converted to xe2x80x94CF3 and becomes thermally stable. Also iodine bonded to the fluorine-containing elastomer and fluorine-containing multi-segment polymer obtained by iodine transfer polymerization can be removed below a detection limit.
The minimizing agent of the present invention can minimize a size of spherulite formed in the crystalline fluorine-containing resin and thus can enhance smoothness of a surface of molded article. Particularly when the fluorine-containing multi-segment polymer is used, falling away of the minimizing agent can be inhibited, which contributes to an increase in cleanliness.
The present invention also relates to the crystalline fluorine-containing resin composition prepared by blending the minimizing agent into a melt-processable crystalline fluorine-containing resin.
The melt-processable crystalline fluorine-containing resin is a fluorine-containing resin having a melting peak temperature (Tm) and crystallizing peak temperature (Tc) which are determined according to DSC, as mentioned above, and forming coarse spherulites at crystallizing. Examples thereof are crystalline PFA copolymers, PVdF polymers, PCTFE polymers, and the like. Preferred melt-processable crystalline PFA which exhibits a remarkable effect of minimizing spherulite size is a PFA having a PAVE content of not more than 10% by weight (4% by mole) and not less than 1% by weight (0.37% by mole) from the viewpoint of heat resistance and chemical resistance. When more than 10% by weight, a melting point (Tm, Tc) decreases and heat resistance is low. On the other hand, when less than 1% by weight, the resulting polymer is a so-called modified PTFE having no melt-processability. A preferred melt-processable crystalline PFA is one having a melt flow rate (372xc2x0 C.xc2x11xc2x0 C., load of 5 kg) of 0.5 to 500 g/10 min, particularly 0.5 to 50 g/10 min. Examples of PAVE are PMVE, PEVE, PPVE, perfluoro(isobutyl vinyl ether), and the like as mentioned above. Particularly PPVE is preferred from the viewpoint of excellent mechanical properties.
It is preferable that an adding amount of the minimizing agent (amount of the amorphous segment (A) in case of the fluorine-containing multi-segment polymer) is from 0.1 to 50 parts on the basis of 100 parts of the crystalline fluorine-containing resin. In the present invention, there is a tendency that the spherulite size decreases when an adding amount of the minimizing agent is increased. However when the amount exceeds 20 parts, there is almost no change in the spherulite size, and when more than 50 parts, hardness and mechanical properties of the obtained crystalline fluorine-containing resin composition are lowered. Therefore an upper limit of the adding amount is 50 parts, particularly 20 parts, further preferably 10 parts. A lower limit thereof is 0.1 part, preferably 0.25 part in which an effect of minimizing spherulite size is obtained.
With respect to an effect of the crystalline segment (B) in case where the fluorine-containing multi-segment polymer is used, there is a tendency that when an amount of the crystalline segment (B) exceeds 50 parts, crystallinity of the crystalline fluorine-containing resin composition is increased and a tensile strength and flexural endurance of the obtained molded article are lowered.
It is basically better not to add other additives to the resin composition of the present invention which is mainly directed to smoothness of a surface of a molded article. However in the fields other than production of semi-conductors, carbon black, titanium oxide, glass fiber, and the like may be added for the purposes of reinforcement and lowering of electrostatic charge.
The crystalline fluorine-containing resin composition of the present invention can be prepared by known processes such as a process in which the agent for minimizing spherulite size is melt-kneaded with the crystalline fluorine-containing resin to give pellets; a process in which pellets or powder of the agent for minimizing spherulite size and a pellet or powder of crystalline fluorine-containing resin are dry-blended; and a process in which an aqueous dispersion of crystalline fluorine-containing resin and a powder or aqueous dispersion of the agent for minimizing spherulite size are wet-blended and then dried. In addition, the crystalline fluorine-containing resin composition containing the agent for minimizing spherulite size may also be prepared by carrying out the polymerization of crystalline fluorine-containing resin in the presence of fine particles of the agent for minimizing spherulite size in the polymerization system. Among those processes, the melt-kneading process or wet-blending process is preferred from economical point of view and from the point that a uniform composition can be obtained.
The agent for minimizing spherulite size of the present invention is excellent in dispersibility into the crystalline fluorine-containing resin despite that it is amorphous. Particularly the fluorine-containing multi-segment polymer gives a more uniform composition since its crystalline segment enhances affinity (compatibility) more. In case where the agent for minimizing spherulite size is used in the form of an aqueous dispersion, it is preferable that the agent comprises fine particles having an average particle size of from 0.05 to 1 xcexcm, and in case where the agent for minimizing spherulite size is used in the form of a powder, it is preferable that the agent comprises particles having an average particle size of from several microns to several tens of microns.
Also when the crystalline fluorine-containing resin composition of the present invention is used particularly in the field of production of semi-conductors, it is preferable to carry out the above-mentioned fluorinating treatment in order to stabilize its unstable end group and reduce an amount of elution of fluorine ion (JP-B-8-30097, JP-A-4-20507).
The crystalline fluorine-containing resin composition of the present invention is melt-processable, and various melt-molding methods such as melt-extrusion molding, injection molding and heat-compression molding can be applied thereto. In those melt-molding methods, spherulites are formed when the crystalline fluorine-containing resin once melted is re-crystallized. By previously blending the agent for minimizing spherulite size of the present invention into the resin, the spherulites to be formed at re-crystallizing can be minimized. For example, in case where a crystalline PFA is slowly cooled under the conditions described hereinafter for measurement of an average size of spherulites, the average size of spherulites is from about 30 xcexcm to about 60 xcexcm when the minimizing agent is not blended. But when the minimizing agent of the present invention is blended, the average particle size can be decreased to not more than 20 xcexcm, particularly not more than 10 xcexcm.
The present invention then relates to a molded article obtained by melt-molding the above-mentioned crystalline fluorine-containing resin composition. The molded article of the present invention is one having an average spherulite size of not more than 5 xcexcm, and has a smooth surface. Particularly when fluorine-containing resins (PFA, PVdF, and the like) having a poor through sight are used as a matrix resin, not only a through sight is improved but also transparency is enhanced. Therefore the molded article is useful as a material for window for inside observation.
Also when the fluorine-containing multi-segment polymer is used as the minimizing agent, since the crystalline segment makes an anchoring function, falling away of the minimizing agent is reduced and generation of particles causing contamination can be inhibited.
The molded article of the present invention can have various forms depending on the molding method, for example, the form of a tube, film, sheet, plate, container or parts in compliance with a variety of purposes.
Since those molded articles of the present invention have heat resistance and chemical resistance of the fluorine-containing resin and the surface thereof is smooth, they can be used suitably as various parts, pipes and containers particularly for producing semi-conductors which are required to be free from contamination.
The present invention is then explained by means of examples, but is not limited to them.
In examples and comparative examples, various physical properties are measured, and the methods of measurements are as follows.
(Content of PAVE)
The content of PAVE is calculated by 19F-NMR method.
(Melting peak temperature Tm and crystallizing peak temperature Tc)
Measurement is made with a differential scanning calorimeter (DSC, Model RDC220 available from Seiko Denshi Kabushiki Kaisha) by using a sample of 3 mg. First the sample is heated up from 200xc2x0 C. to 350xc2x0 C. at a rate of 10xc2x0 C./min, and after kept at 350xc2x0 C. for one minute, cooled down to 200xc2x0 C. at a rate of 10xc2x0 C./min. A crystallizing peak temperature (Tc) is determined from a crystallizing curve obtained at that time. Further after the sample is cooled down to 200xc2x0 C. and kept at 200xc2x0 C. for one minute, it is again heated up to 350xc2x0 C. at a rate of 10xc2x0 C./min. A melting peak temperature (Tm) is determined from a melting curve obtained at that time.
(Glass transition temperature Tg)
The sample of 10 mg is heated up from xe2x88x9270xc2x0 C. to 110xc2x0 C. at a rate of 20xc2x0 C./min, and then cooled down to xe2x88x9270xc2x0 C. at a rate of 20xc2x0 C./min by using the above-mentioned differential scanning calorimeter. The sample is again heated up to 110xc2x0 C. at a rate of 20xc2x0 C./min. A glass transition temperature (center point) is determined from a curve obtained at that time.
(Average size of spherulite)
A disk-like sample sliced to a thickness of about 50 xcexcm is put on a slide glass which is then mounted on Model FP82HT Hot Stage (available from Mettler-Toledo AG). The sample is melted by heating up to 360xc2x0 C. at a rate of 40xc2x0 C./min and held at 360xc2x0 C. for three minutes, followed by cooling down to 200xc2x0 C. at a rate of 10xc2x0 C./min to be re-crystallized. After the sample on the slide glass is removed from the Hot Stage, it is allowed to be cooled down to room temperature. The measurement is made with an optical microscope (xc3x97140) by measuring diameters of continuous 30 spherulites among those observed on the surface of the sample while the spherulites are recognized by means of polarized light. The particle size is an average of those 30 spherulites. With respect to the molded article in the form of tube, the surface of the sample is observed with a scanning electron microscope (xc3x971,000 to xc3x975,000), and the average size of spherulites is determined by measuring diameters of continuous 30 spherulites in the same manner as above.
(Mooney viscosity: ML1+10)
Measurement is made in accordance with JIS K 6300 by using a Mooney viscometer available from Kabushiki Kaisha Ueshima Seisakusho.
(Intrinsic viscosity: xe2x80x9cxcex7xe2x80x9d)
Intrinsic viscosity is determined by measuring at 35xc2x0 C. by using FC-75 available from Three M Co., Ltd.
(Melt flow rate: MFR)
Measurement is made at 372xc2x0 C. at a load of 5 kg in accordance with ASTM D 2116.
(Thermogravimetric analysis)
A weight loss is measured by heating a sample of 10 mg from 20xc2x0 C. to 600xc2x0 C. at a rate of 10xc2x0 C./min with flowing 200 ml of air by using a differential scanning calorimeter (RDC220 available from Seiko Denshi Kabushiki Kaisha).
(Surface roughness)
A roughness of inner surface of a tube (arithmetic mean roughness (Ra) and maximum height (Ry)) is measured in accordance with JIS-B0601 by using a contact type surface roughness meter (SURFTEST600 available from Kabushiki Kaisha Mitutoyo).